Field of the Invention--This invention relates to the degasification of liquids and the simultaneous imparting of the dynamic force to convey the liquid to its ultimate point of use. It also relates to novel methods for controlling the natural conditions attendant to the degasification of liquids and the withdrawal of the products which have contaminated the liquid so as to assure the delivery of a degasified liquid of determinable quality on a continuous basis.
Description of the Prior Art--The disadvantages of entrained and dissolved air and gases in liquids have long been recognized. Such air and gases cause corrosion of metals, vapor bind systems in which the liquids are being utilized, and in the case of liquids used as the basic medium in production processes, can effect both the quality of an end product and the reaction characteristics of the several reactants in the process. Numerous gases may also contribute to atmosheric pollution. Typical are the gases produced by the burning of fossil fuels or heating air to extremely high temperatures.
Several methods of degasification are in current use, a brief description of each follows:
(a) Counterflow Scavenging--A scavenging gas that is not in the liquid to be degasified is passed counterflow in a vertical chamber through the contaminated and downcoming liquid. Air is most commonly used as the scavenger. The dissolved gases in the liquid are rejected to the upflowing air, this by reason of the partial pressure phenomenon. An example of this type of degasification is the liberation of carbon dioxide from waters containing high bicarbonate alkalinity which have been treated with the direct application of acid or have been passed through an ion exchanger employing the principle of cation exchange on the hydrogen cycle. The carbon dioxide laden waters are introduced into the top of a vented chamber which is packed with various media to cause the break-up of the water into droplets. Forced air is introduced at the bottom of the chamber, and in rising to the vent, is infused with the carbon dioxide because the partial pressure of the gas as it exists in the liquid is greater than the pressure exerted by the minute quantities of carbon dioxide as it exists in the air. A deaerating feedwater heater is but a variation of the counterflow type degasifier. Steam replaces air as the scavenging agent and in addition to being the carrier of the rejected gases, the steam serves to unbalance saturation in favor of the vapor state of the liquid being degasified. This by elevating the temperature of the liquid. Decarbonates are also a form of counterflow degasifiers. The simplest form of which is illustrated by blowing air through a straw which has its lower end submerged in a carbonated beverage. Process decarbonating equipment involves the arrangement of a series of perforated conduit at the bottom of a vented vessel which contains the liquid to be degasified. A scavenging gas is introduced into the conduit and in rising through the liquid, unbalances the partial pressures being exerted by the several gases in the liquid. A primary deficiency of these devices, excepting the feedwater heater, is the recontamination of the liquid with the scavenging gas.
(b) Degasification by Vacuum Stripping--The method involves an apparatus similar to that used in counterflow scavenging. Contaminated liquid is introduced into the top of a closed column and passes downward over a series of slotted trays, dispersing the liquid into droplets. This action increases the surface area of the liquid to promote the release of dissolved gases upon application of sub-atmospheric pressures. External eductors create a reduced pressure which is applied at a number of openings along the vertical axis of the degasifier column. Gases liberated from the liquid are drawn from the column at these points and are ultimately discharged to the atmosphere. In such a process, the initial cost of the equipment and continued operating costs are high and the degree of degasification leaves much to be desired. In particular, it is difficult to evacuate gases from the interior areas of the column and the liquid is recontaminated in its downward progress by the gases which have been liberated at the lower levels of the column.
(c) Toricelli Method(so called because it applies to the principle developed by Toricelli in the invention of the barometer, i.e., evacuating a sealed container)--Liquid is pumped from a sealed container on a batch basis. Repeated redissolving of gases is a strong adverse factor in the Toricelli method of degasification. The gases which have been liberated by reason of sub-atomspheric pressure boiling on pump-down, redissolve in the incoming batch of contaminated liquid.
(d) Chemical Treatment--Chemical compounds have been developed to either neutralize or change the state of gases in liquids or to apply a protective film to systems materials. Chemical treatment is, in most cases, expensive and is difficult to apply in proper proportions to afford a continuous high level of protection. Where low dissolved solids concentrations in the liquid is a requirement, chemical treatment is not advisable because the additive compounds or the products of their reaction with the contaminant gases contribute substantially to the total solids in the liquid. Corrosion control compounds, particularly those in the amine, chromate, and sulfite groupings, are either toxic or deplete oxygen residuals in water. In recent years numerous pollution control authorities have enacted legislation prohibiting the indiscriminate discharge of such compounds into normal drainage facilities and natural water courses. Solids concentration control through continuous or intermittent blowdown is an example of such discharge.